The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Disclosed are compositions and methods for treating subterranean formations, in particular, oilfield stimulation compositions and methods using polymer crosslinked with ionic complexes to viscosify the treatment fluid.
High volumes of formation fracturing and other well treatment fluids are commonly thickened with polymers such as guar gum, the viscosity of which is greatly enhanced by crosslinking with an ionic complex, for example of boron or metal such as chromium, aluminum, hafnium, antimony, etc., more commonly a Group 4 metal such as zirconium or titanium. In reference to Periodic Table “Groups,” the new IUPAC numbering scheme for the Periodic Table Groups is used as found in HAWLEY'S CONDENSED CHEMICAL DICTIONARY, p. 888 (11th ed. 1987).
During hydraulic fracturing treatments, fluids with high viscosity are needed to create hydraulic fracture as well as transport proppants into the fracture. After the treatment is completed, however, it is necessary that the viscous fluid be broken to facilitate flow back to the surface without bringing back proppants.
Oxidizing agents such as persulfates or bromates are commonly used to break fluids thickened with polymers such as guar. It is widely understood that the mechanism is associated with the breaking of polymer through radical type chain scission reactions. Very often, encapsulated oxidizing agents are used in order that fracturing fluids are not broken prematurely. While oxidizers work effectively in reducing fluid viscosity, it has been observed that the oxidized polymer based fluid often contains insoluble materials which may lead to damaged formation and/or fracture conductivity. Enzymes and the lowering of pH are also sometimes used to break polymer fluids downhole.
Excessive crosslinking of polymers, also known as overcrosslinking, which has accidentally occurred in an uncontrollable manner in the laboratory, is normally avoided in the field, where oxidizers, enzymes and pH lowering agents are the most commonly used breakers.